package train48days;

import java.util.Scanner;

public class 养兔子 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long[] arr = new long[91];
        arr[1]=1;
        arr[2]=2;
        for (int i = 3; i <=91 ; i++) {
            arr[i]=arr[i-1]+arr[i-2];
        }
        while (sc.hasNext()){
            int n =sc.nextInt();
            System.out.println(arr[n]);
        }
    }
}
